This invention relates to improved properties of materials for making body supporting splints, casts, brassieres, belts, athletic supporters, headphones, ear plugs, impression casting material for dentists, masks, models, art molds, toys, golf balls, tires and other plastic and rubber items, including moldable items storable in rolls, stacks or sheets or moldings from which individual moldable elements are readily separated and formed into shapes for such uses as listed.
Plastic materials have been successfully used in the past for making splints, casts and the like. U.S. Pat. No. 3,490,444 describes the use of thermoplastic polydienes like transpolyisoprene and transpolychloroprene which melt between 60.degree. C. and 100.degree. C. and harden by crystallization at about 40.degree. C. whereby this can be formed for use as a body supporting member. An important feature of that invention is the incorporation of a filler (e.g. short lengths of fiber) such that the final product would be free of substantial creep or deformation under long periods of use below about 40.degree. C. Other polymers melting between 50.degree. C. and 110.degree. C. and hardening by crystallization have also been recommended. U.S. Pat. No. 3,604,413 recommends copolymers of trioxane and several other polymers. Poly (epsilon-caprolactone)(PCL) has also been found to be an excellent splint or cast material (U.S. Pat. No. 4,144,223). Polyurethanes based on prepolymers of poly (epsilon-caprolactone) have also been used (U.S. Pat. No. 4,316,457).
As described in earlier patents, the polymers can be heated in hot water at a temperature usually exceeding 50.degree. C. and up to about 100.degree. C., whereby they become soft, self-adherent and pliable sufficient to be deformed and shaped as a cast or splint or protective device. When allowed to cool in air to about 40.degree. C., the materials remain pliable, moldable and cohesive for a period of several minutes, exhibiting a hysteresis, as described in U.S. Pat. No. Re 30,541. During this time the splint, cast or device can be molded directly to the patient without discomfort, whereupon the so shaped plastic hard sets by crystallization to assume a rigid form as a useful body support member or protective device.
Poly (epsilon-caprolactone) is an excellent splint or cast material by itself and in blends with common, fine particle size fillers and pigments, such as silica, diatomaceous earth, clay, and titanium dioxide. The filler may be present in the blends at a concentration of from about 1 to about 30 parts by weight per 100 parts by weight of the poly (epsilon-caprolactone). Mixtures of the fillers may also be used, especially of silica and titanium dioxide, which impart a desirable white color to the compound.
Poly (epsilon-caprolactone) (PCL) makes an excellent cast or splint, in the hardened state. However, the heat-softened material is difficult to handle because it is fluid and sticky. This can be overcome by adding reinforcing fibers, cheesecloth (to support the plastic), or by blending PCL with a polymer like Transpolyisoprene (TPI), which is more elastic in the heat softened state.
Applicant Lester Larson has conducted laboratory investigations of the properties of PCL-TPI blends. The stickiness of heat-softened PCL disappears at around 50--50 mixtures, but other properties (e.g. tensile strength) are better when 75 % or more of the blend is Transpolyisoprene. Pure PCL is good in respect to hardness, strength, hysteresis, and it has the advantage of being transparent in the heat-softened state. Fluidity and stickiness are its drawbacks. It has been found that this softened state fluidity is reduced by electron radiation of thin sheets of the polymer (U.S. Pat. No. 4,240, 415).
U.S. Pat. No. 4,144,223 demonstrates blends containing 50 to 98 parts by weight of Transpolyisoprene along with 2 to 50 parts by weight of Poly (epsilon-caprolactone), for use as medical splints and as golf ball covers. It further mentions the need to vulcanize or "cure" such a blend for use as a golf ball cover.
Gamma radiation is commonly used as a sterilization method for hospital items such as catheters, surgical items and critical care tools. Gamma radiation is also commonly used to kill bacteria in commercially sold items such as pacifiers, nipples, baby bottles, and even food items such as strawberries, chicken, and dog food. Safe techniques for using gamma radiation are well understood and in common use at licensed sterilizing facilities throughout the United States and other industrialized countries.